OpenAPI

Our services are implemented using the NestJS framework which includes SwaggerUI/OpenAPI support. We should always include an OpenAPI document for our public REST services and use the SwaggerUI to make it accessible.

Our infra-nest-server.bootstrap accepts a parameter of type OpenAPIObject which is used to configure the SwaggerUI. The service should set the base properties in openApi.ts and then use NestJS OpenAPI Decorators on controllers, methods, models and DTOs.

Example of openApi.ts

import { DocumentBuilder } from '@nestjs/swagger'

export const openApi = new DocumentBuilder()
  .setTitle('IdentityServer Public API')
  .setDescription(
    'Public API for IdentityServer.\n\n\nThe swagger document can be downloaded by appending `-json` to the last path segment.',
  )
  .addServer(process.env.PUBLIC_URL ?? 'http://localhost:3370')
  .setVersion('1.0')
  .build()

For more details about OpenAPI support in NestJS read their docs.

Download the OpenAPI document

The SwaggerUI makes the document itself accessible on the same path with -json added. For example if the SwaggerUI is rendered on https://innskra.island.is/api/swagger then the document can be downloaded from https://innskra.island.is/api/swagger-json.

As the SwaggerUI is missing a download button, we should include a short message in the description field, how the document can be downloaded. This helps our service consumers to get the document for client and model generation.

Setting server property

In the openApi.ts example above, we add the server property. To get the environment specific host details we use the environment variable PUBLIC_URL. This variable needs to be set in the service infra dsl (or helm chart if it's not yet part of the monorepo infra namespaces).

Configuring SwaggerUI dependencies for esbuild

As we use esbuild to build and bundle our APIs, we need to add swagger-ui-dist to the external list in esbuild.json for our SwaggerUI to work in a production build.